"I am not denying the importance of fighting climate change and global warming, unlike Donald Trump, who may just have taken the most serious, and wrong, decision on climate change this world has seen," Hawking said last year about the Paris withdrawal.

In a 2016 lecture, he predicted that humanity has only 1,000 years left on Earth and we must find another planet to live on.

"[W]e must ... continue to go into space for the future of humanity," Hawking said. "I don't think we will survive another 1,000 years without escaping beyond our fragile planet."

According to Hawking, Earth and its inhabitants could soon be doomed. But, as he wrote in 2016, he's actually an "enormous optimist" for our future—that is, if we can learn to work together.

"Perhaps in a few hundred years, we will have established human colonies amid the stars, but right now we only have one planet, and we need to work together to protect it," he wrote. "To do that, we need to break down, not build up, barriers within and between nations."

"We can do this, I am an enormous optimist for my species; but it will require the elites, from London to Harvard, from Cambridge to Hollywood, to learn the lessons of the past year. To learn above all a measure of humility."

Hawking died from complications of Lou Gehrig's disease, which he suffered from since he was 20.

Sixteen-year-old climate action leader Greta Thunberg stood alongside European Commission President Jean-Claude Juncker Thursday in Brussels as he indicated—after weeks of climate strikes around the world inspired by the Swedish teenager—that the European Union has heard the demands of young people and pledged more than $1 trillion over the next seven years to address the crisis of a rapidly heating planet.

In the financial period beginning in 2021, Juncker said, the EU will devote a quarter of its budget to solving the crisis.

A new study reveals the health risks posed by the making, use and disposal of plastics. Jeffrey Phelps / Getty Images

With eight million metric tons of plastic entering the world's oceans every year, there is growing concern about the proliferation of plastics in the environment. Despite this, surprisingly little is known about the full impact of plastic pollution on human health.

But a first-of-its-kind study released Tuesday sets out to change that. The study, Plastic & Health: The Hidden Costs of a Plastic Planet, is especially groundbreaking because it looks at the health impacts of every stage in the life cycle of plastics, from the extraction of the fossil fuels that make them to their permanence in the environment. While previous studies have focused on particular products, manufacturing processes or moments in the creation and use of plastics, this study shows that plastics pose serious health risks at every stage in their production, use and disposal.